I saw that Valvoline has a Synthentic blend gear oil (75w- 90) the bottle says its GL-5 SAE rated. Is this stuff ok to run in the diffs?

 

Yes it will work great. Any GL-5 rated 75w90 Synthetic gear oil will work and is what is recommended. I've had great luck with Mobil 1, but I wouldn't hesitate to run valvoline in it.

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I would imagine a blend would work fine, but if it is under warranty I think the book calls for full synthetic that meets GL-5.

I've got Redline (full synthetic) in this truck, which I also ran in my last truck, both with good results.

 

On my next diff oil change, I'll run the blend in the front since it doesn't get the work the rear does. I also happen to have 3 quarts of it already.

 

They also have 85-140 in the blend. I think the bottles are blue and they are half the price of full synthentic.